Resistor unit and method of forming same



Feb. 16, 1932. L. BRADLEY I 1,845,828

7 RESISTOR UNIT AND METHOD OF FORMING sun:

Filed Aug. 19. 1925 IQ/nil; Earadlay Patented Feb. 16, 1932 UNITED- STATES PATENT or? LYNDE BRADLEY, O1 MILWAUKEE, WISCONSIN, ASSIGNOB BY IEBNE ASSIGNMENTS,

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TO ALLEN-BRADLEY COMPANY, OF MILWAUKEE, WISCONSIN, A CORPORATION 01' WISCONSIN mISTOB/ UNIT AND METHOD FORMING sum Application filed August 18, 1925. Serial No. 51,278.

- This invention has as one of itsob'ects the provision of an improved resistor unit which is especially adapted for use in radio receiving and broadcasting apparatus, or which may be employed in any other situation where a resistor unit is desirable.

Another object of this invention resides in the provision of a compressible resistor unit having a low internal resistance and a lo high contact or microphonic resistance, so

that a column of units will have, a comparatively low resistance under maximum pres sure in comparison to their resistance under minimum or no pressure, thus giving a greater range of .variation of resistance under varying pressures.

A further object of this invention resides in the provision of an improved apparatus for forming resistor units in accordance with this invention in an economical and practical manner.

With the above and other objects in view which will appear as the description proceeds, my invention resides in the novel method, construction, combination and arrangement of parts substantially as hereinafter dey scribed and more particularly defined by the appended claims, it being such changes in the preclse embodiment of so the hereindisclosed invention may be made as come within the scope of the claim;

, In the accompanying drawings, I have illustrated several completeexamples of the physical embodiment of my invention constructed according-to the best modes I have so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a fragmentary view, partly in section and partly in elevation, of a diagrammatic illustration of a shaped resistor units;

Figure 2 is a view similar to Figure 1 illustrating the completion and ejection of the disc unit;

Figure 3 is a side view of a stack of discshaped resistor units wrapped prior to re ceiving treatment in the presence of heat.

part of the wrapping being broken away;

Figure 4"is'a' side view of a clamp or compression member which may be applied to the understood thatv press for forming discwrapped stacks of disc-shaped resistor units Y to maintaln the same under pressure during the heat treatment;

' Figure 5 is a perspective view of an apparatus employed to subject the units 'to the influence of an electric current having the power or capacity to reduce the specific or in- 'ternal resistance of the units, a diagrammagic view of one wiring circuit'being shown,

Figure 6 is a view, partly in elevation and partly in section of a modified form of reslstor unit.

. The resistor unit illustrated in Figures 1 to 5, inclusive, is especially adapted to' be arranged in stacks or piles to form the resistor these characteristics will give a greater spread or range from minimum to maximum as the method of treating or shooting the discs. hereinafter described, eliminates. the resistance that heretofore could not be squeezed out. In the unit illustrated in Figure 6, it is also desirable that its internal resistance be fixed or unchangeable under nor .mal conditions, and it .is also of the utmost importance that its resistance be capable of calibration. The method oi calibrating the resistance is closely allied to the method of shooting the discs and is'described in detail in my copending application, Serial No. 53.570, filed Aug. 31, 1925. 4

Referring now more particularly to the accompanying drawings in which like numerals designate like parts throughout the several views, the numeral 5 designates the bed plate of a forming machine having a female die 6 mounted therein and cooperating with a male die or compression plunger 7 which is movable therein to compress materials, to be later described, and form the unit 8, which is removed from the die by an tion of the plunger to eject the unit 8 formed by the compressing of the substance, to be later described, forming the unit into disc shape, the unit being removed from between the compression plunger and ejector by an automatic finger member 10.

The resistance unit, while illustrated in Figures 1 to 5, inclusive, as of disc shape, may be formed as illustrated in Figure 6, or in my co-pending application filed therewith, or in any desired shape. The units are preferably formed from an organic substance having a conductor mixed therein and the following ingredients and proportions have been found by experience to produce a highly citicient unit: I

Formula for high resistance unit:

Graphite #1 AF 3% 545 grams Asbestos powder #1250 4 pounds Phenolic condensation product 87% 34 pounds, 13 ozs.

Formula for low resistance unit: I

Graphite #1 AF 10% 1816 grams Asbestos powder #1250 10% 4 pounds Phenolic condensation product #60 80% 32 pounds dered asbestos with the dry, powdered phenolic condensation product.

" Second Wetting the mixture thoroughly with denatured alcohol to dissolve the phenolic condensation product.

Third :Grind ing the wet mixture to make a thoroughly homogeneous mixture, also to form the mass .into long, thin strings so it may be dried much more readily.

Fourth :Removing the alcohol by heat and vacuum. I

Fifth :Pulverizing product.

Sixth :Dry-mixing the powder to make it absolutely uniform.

Seventh :Blending mixtures containing and sifting the dried different percentages of graphite in order to obtain mixtures which will give required resistances when molded into units.

The discs 8 resulting from the compression of the composition previously described are arranged in stacks ofalternate resistor discs and separators 11, preferablyfof carbon, and wrapped with a suitable covering 12 such as heavy paper or the like. The stack of discs is then heat treated, being placed in an oven ma ntained at 400 degrees Fahrenheit 'for a period of two hours and then allowed to cool. If desired the stack maybe secured iii a clamping mechanism 13 to maintain the same under pressure during the heat treatment.

Upon removal from the heatin oven the units are complete and ma be use in a resistor column, but their speci c or internal resistance is high, and forvbetter results and increased spread or variation of contact resistance through variations of pressure, it is necessary that their internal resistance be materially lowered. Tests have proven that resistor units subjected to the method hereinafter described have their internal or specific resistance materially lowered.

The unit 8 is, therefore, subjected to the influence of an electrical current having the power or capacity to change the characteris- V tics thereof to the extent of reducing its specific or internal resistance and at the same time maintaining its high contact or microphonic resistance. It has been found that a current that oscillates and is of high potential, or high frequency has the power to so change the characteristics of a resistor unit to obtain the desired results, although it is to be understood that any current having the capacity or power to produce the desired results may be employed, and in Figure 5 I have illustrated one embodiment of a machine for subjecting resistor units to the influence of such a current.

An endless belt 14' is preferably trained about a relatively large idle pulley 15 and a relatively small drive pulley 16, the upper or top-most portions of which are substantially horizontally aligned to maintain the upper stretch 17 of the belt on a horizontal p ane.

The idle pulley 15 is mounted on a shaft 18 supported in standards or mountings 19 and the drive pulley 16 is fixed on a drive shaft,

20 connected with a gear reduction unit 21. The drive shaft 22 of the unit 21 has a pulley 23 mounted thereon which is driven by a. belt 24, trained about it and the drive ulley 25 of. a motor 26. The relative sizes 0 the'pulleys 23 and 25, and the pulleys-15 and 16 and the gear reduction 21 cause the belt 14 to advance at a relatively slow speed.

The end of the belt trained about the pulley 15 is the receiving end and mounted thereover on a suitable support 27 is a tray 28 having a discharge opening 29 from which extends a guide 30. The guide lies close to the upper stretch of the belt and the units 8 are I j moved thereover from the tray onto the pulley 14 by an operator, a belt support 31 being.

mounted under the guide 30, as illustrated.

As the upper stretch of the belt moves from the pulley 15 to the pulley 16, the units thereon are subjected to the influence of a current having the power or capacity to reduce the internal resistance of the unit. This is accomplished in the present embodiment by means of pairs of contact members 32 and 33 forming spark gaps through which the upper Stretch of the belt-and the units 8-thereon pass as the current jumps from one contact to the other of each pair.

The contacts of each pair are supported from an oscillating lever 34, the up er-most contact being preferably adjustab e by a screw or other means 35 to regulatethe length of the spark gap. The lever 34 is supported from a shaft 36 journaled at one end in a bearing 37 and at its other end in a bearin 38, an actuating lever 39 having one end fixed to the shaft and its other end 40 held in engagement with a rotating eccentric 41 fixed on the shaft22, by a spring 42. The shaft 22 being constantly rotated as the belt is advanced, rapidly oscillates the lever 34 to move --the contacts across substantially the entire width of the belt to insure the passing of the units through the path of the current flowing across the spark gaps. But one pair of contacts may be used, but the provision of more than one insures each unit coming within the influence of the current flowing across the contacts. 7

The circuit illustrated in connection with the present embodiment of my invention consists of a spark coil 43 which maybe of conventional construction having a primary coil 44 and a secondary coil 45, the primary coil being connected with a source of energy 46 by conductors 47 and 48, a controlling switch 49 located within one of the conductors to permitthe disru tion of the circuit. end of the secon ary coil is connected with the up r contact of one pair by a conductor 50 and the other end thereof is connected with the lower contact of the pair by a conductor 51. 'A single coil or circuit may be employed if desired for both pairs of contacts, although a se arate circuit for each contact is illustrate After-the units have been subjected to the influence of the current flowin across the spark gap and consequently filrough the units, they are discharged automatically from the belt at its dischar e endinto a container 52. The finished unlts may, after being treated as above described have their scorched or punctured surfaces burnished orsmoothed to restore them to their original microphonic condition before being incorporated in a compressible resistor or any One a bod 53 formed of the ingredients above descri ed and molded under pressure with end caps or contact members 54 which facilitate their connection in an electric circuit. The resistance 0 the unit illustrated in Figure 6 is reduce by subjecting the same to the influence of a current having the power or capacity to so change the unit characteristics.

As above described, the subjecting of a unit of the character described to the influence of a current of the desired characteristics so acts on the unit as to reduce its resistance and permits the calibration of the resistance to a roximately any predetermined value, w lch it holds a must change. The method and apparatus gr calibrating the resistance of the unit at approximately any desired redetermined degree is better described and illustrated in my co-pending application above referredto. rom the foregoing description taken in connection with the accompanying drawings, it will be readily apparent to those skilled in the art to which an invention of this character appertains that I provide a very novel and improved resistor unit and method of and apparatus for forming same whereby fithe unit is very efficient and reliable and can be very efliciently produced. I claim:

The method of forming a resistor unit, which consists in molding the same from a mixture of 86 parts phenolic condensation product, 10 parts asbestos and 4 parts graphite and in heat treating the unit.

In testimony whereof I aflix my si LYNDE BRAD aturc.

other type of device with which'the same is adapted to be used. The restoring of' the original micro honic condition of the discs can be accom lished by any ordinary smoothing or polis ing device, but in practice it has been found satisfactory to merely tumble the discs in a revolving drum.-

- In Figure 6 another type of resistor unit is illustrated, which is more particularly described and claimedin my application filed herewith and which is especially designed for use as a fixed resistance unit in contradistinction to the use of the type'of unit hereinabove described. This unit consists of 

